Harvesting machines of the above kind, such as forage harvesters, baling presses or forage wagons, are equipped with cutting devices for cutting and/or chopping the harvested crop. Such cutting devices are also used on harvester-threshers to chop the threshed straw, if desired. For the cutting results it is important that the edge or edges of the cutting device are sufficiently sharp. In the case of dull edges the energy that is required for the cutting operation increases. If the harvested crop is not chopped in a freely cutting manner, i.e. without the use of a counter-cutter, a counter-cutter may be useful. The distance between the counter-cutter and the edge is likewise critical and should be adjusted as accurately as possible.
In the currently commercially available harvesting machines it is up to the driver to decide whether and when a sharpening operation of the edge occurs. Adjustment of the counter-cutter currently also only occurs at the request of the driver.
In various publications devices have been described for determining the sharpness of chopping blades. Pursuant to DE 40 23 113 A and DE 40 23 114 A the tension induced by the edges in inductive transmitters is evaluated. DE 199 03 153 A suggests the detection of the cutting forces. DE 102 35 919 A and DE 103 03 504 A reveal the mechanical detection of vibrations of the counter-cutter to determine sharpness.
To measure the distance between the edges and the counter-cutter a series of devices have been suggested (DE 41 34 957 A, DE 43 35 786 A, EP 0 706 752 A), in which a vibration sensor is attached on the counter-cutter, the output signal of which sensor is a function of the distance between the counter-cutter and the chopping blades. To measure the distance between the counter-cutter and the chopping blades moreover also magnetic sensors are known, which comprise a permanent magnet that is connected with the counter-cutter and an induction coil, in which the passing chopping blades induce an electro-motive force, which is amplified and detected (EP 0 943 888 A).
DE 38 16 206 A describes a cutting device for double fabrics, which comprises a knife, whose exact positioning and sharpness is examined by means of an opto-electrical sensor. It is composed of a camera, which detects the knife, and an electronic evaluating unit. Said publication discloses no suggestions for using the sensor in an agricultural harvesting machine.
Furthermore a series of publications is available in which the harvested crop is monitored visually. U.S. Pat. No. 6,119,442 A describes a harvester-thresher, in which a camera is directed at the harvested crop being processed. The camera signals are evaluated and compared to target values. The operating parameters of the harvester-thresh are modified as a function of the results of the comparison. EP 1 053 671 A suggests to examine the chopped harvested crop by means of a sensor operating in the near infrared region so as to detect contents. The measurement values of the sensors can also be used to deduce characteristics of the harvested crop, such as crude fiber content or fiber length. These publications do not reveal that the signals of the optical sensors are suitable for determining sharpness or for measuring the distance between the counter-cutter and edge.